Measurement of isolated-photon pair production in pp collisions at √s = 7 TeV with the ATLAS detector

Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title> <jats:p>The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at <jats:inline-formula> <jats:tex-math>$ \sqrt{s}=7\;\mathrm{TeV} $</jats:tex-math> </jats:inline-formula>. The full data set collected in 2011, corresponding to an integrated luminosity of 4<jats:italic>.</jats:italic>9 fb<jats:sup>−1</jats:sup>, is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|<jats:italic>η</jats:italic>| <jats:italic>&lt;</jats:italic> 1<jats:italic>.</jats:italic>37 and 1<jats:italic>.</jats:italic>52 <jats:italic>&lt;</jats:italic> |<jats:italic>η</jats:italic>| <jats:italic>&lt;</jats:italic> 2<jats:italic>.</jats:italic>37) and with an angular separation Δ<jats:italic>R &gt;</jats:italic> 0<jats:italic>.</jats:italic>4, is <jats:inline-formula> <jats:tex-math>$ 44.0_{-4.2}^{+3.2 } $</jats:tex-math> </jats:inline-formula> pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins-Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.</jats:p>